726 Thomsons Turbine. L L lying in the groove M M ; and as the ring Q is revolved, by hand or governor, through gear N, the shutters are completely raised or lowered, according to direction of rotation. In Fig. 713 the actual path of the water is shewn in a Jonval turbine at A, and in a Girard turbine at B, a b being free path and velocity due to guide blades, and b c the wheel velocity; a c is the relative velocity, and shews actual path in general direction. Making c d = 'b c, ad will be the line of wheel vane causing curved water path a <:, the horizontal ordinates of curvature on a d and a c being equal i J//? /?/? ^? £ « fit.' *<. CA"T WK ^ 5 / /v 2 o1 ^ *.* y i^V ^ jx5 V (/; / I % ^v ^ ^""i ,^' y /( ^I > 144 y r i s .Ui s ?£ OP Vtf ^ fu J f Fig. 714 is a diagram shewing comparative efficiencies under varying openings. Although the Girard is usually less efficient than pressure turbines with full sluice, its efficiency is unimpaired by fractional opening, Thomson's Turbine, Fig. 715.Here the supply water A enters the rim of the wheel B, and escapes axially into c the tail race, so the machine is called an inward-flow turbine. Its energy is largely due to pressure, the outlet being either drowned or connected with a suction pipe. Referring to the plan, the guide blades D D are pivoted at E E, and can be moved in or out by the levers and links F F. Then the vertical shafts at F F are all connected, and rotated, through worm gear, by the hand wheel G; thus more or less water mcty be admitted to the wheel. Although the gear is complicated, its action is very perfect, the supply being regulated without materially affecting angle of blades or other conditions, and a nearly maximum efficiency of 75% obtained for -11! onenings. The wheel is shewn in detail at H.